Transcription

1 IJSRD - International Journal for Scientific Research & Development Vol. 3, Issue 11, 2016 ISSN (online): Effect of Aspiration Pressure on Convergent Nozzle Employed for Gas Atomization of Liquid Metals P. Sanjay 1 T.N. Srinivasa 2 1,2 Department of Mechanical Engineering 1,2 AMC Engineering College, Bangalore Abstract Atomization is often chosen as one of powder production techniques because of high production rates and ability to make alloy powders of desired composition. In gas atomization process, liquid metal is broken into droplets to form powders upon solidification. Gas-metal interaction influences the break-up of liquid stream into droplets. The idea is to transfer kinetic energy from a high velocity jet-gas expanded through a nozzle, to a stream of liquid metal, resulting in fragmentation and break up into metal droplets. Gas atomization process is one of the widely used powder production technique and nozzles play an important role in the gas atomization process. The geometry of nozzles governs the gas to metal interaction. The selection of nozzle type and the flow geometry is the most important preset parameter for atomization process. The design of an atomizing nozzle determines degree of contact of liquid metal with the atomizing gas. Aspiration pressure is the optimum pressure developed at tip of the nozzle (at atomization zone) which will favor gas atomization process. In the present analysis, an attempt was made to analyze effect of atomization pressure and aspiration pressure for Convergent nozzle (C-nozzle) employed for gas atomization process using Computational Fluid Dynamics (CFD) techniques Key words: Gas Atomization, Convergent Nozzle, Aspiration Pressure, CFD I. INTRODUCTION A. Gas Atomization Process Gas atomization process helps in production of a wide range of ultra-fine spherical metal powders which have very attractive material properties. In gas atomization process, atomization pressure plays an important role in determining particle size and surface morphology [1]. Atomizing nozzles have co-axially placed Metal Delivery Tube (MDT), which carry molten metal to atomizing zone [2, 3]. The flow properties of gas are considerably affected by the presence of MDT. In this process, inert gas (N2) is used an atomizing medium. Atomization technique has been extensively reviewed by Beddow [4], Grant et al [5] and Lewley [6]. Gas atomization process is one of widely used powder production technique. In gas atomization process, molten metal is melted and liquid metal is broken into individual particles to form powders. Gas atomization is one of the powder production method/technique. In this method, kinetic energy of a high velocity (greater than Mach 1) impinging inert gas jet disintegrates continuous metal flow into droplets. Nozzles are used to achieve the atomization through break-up of molten metal stream into droplets by fast flowing gas [7, 8, 9, 10]. The heart of the gas atomization process is the nozzle. The set-up for gas atomization of liquid metals using a C - nozzle assembly is shown in figure- 1 Fig. 1: Atomization set- up for C-nozzle B. Aspiration Pressure Aspiration Pressure is the pressure developed at the tip of Metal Delivery Tube (MDT). This is the optimum pressure for atomization to occur. Aspiration pressures for various protrusion lengths for C-nozzle is also been measured using CFD trails in gas-only condition (only considering the gas flow without melt flow) and are compared with those obtained from the numerical analysis and experimental results [11]. A protrusion length between 2mm and 3mm is found to be optimum for nozzles with a parallel portion attached at the end of the nozzle. This configuration gives rise to lowest aspiration pressure, which assists in melt flowing out of the MDT. This configuration is very much favorable for gas atomization process. Decrease in aspiration pressure with increase in protrusion length from 0 to 2mm is experimentally verified by available literatures [12]. When atomization gas pressure increases, aspiration pressure also increases and this may not be favorable for atomization process. A good correlation exits between gas only flow condition and melt-gas flow condition. In the present study, based on the closed couple C-nozzle configuration, a computational fluid flow model was used to investigate the effect of gas atomization pressure (P0) on gas flow field along with aspiration pressure [13]. By increasing gas atomization pressure, aspiration pressure also increases which in turn produce a weak sucking action on the melt flow or lead to a low velocity of melt flowing out of crucible. So aspiration pressure is directly affected by stagnation pressure [1]. In the present investigation, configurations considered was a C- nozzle with small parallel portion of various lengths (which is the extension of the MDT) and attached to its end. The analysis shows that pressure, velocity, temperature and density of atomizing gas at the exit of nozzle does not change much for various nozzle configurations, whereas turbulent kinetic energy is drastically reduced when a parallel portion is attached at the end of C-nozzle. All rights reserved by 362

2 II. CFD TRAILS TO OBTAIN OPTIMUM ASPIRATION PRESSURE FOR C-NOZZLE A. Description of physical model and parameters considered for numerical analysis of Mach number for CD nozzle In the present investigation study, CFD trials have been carried on C-nozzle for plotting pressure. Geometric modeling and meshing of C-nozzle were carried out and results were plotted using fluent software. The C-nozzle parameters considered for simulation of 1M (Mach number, sonic) are shown in table s applied were Pressure inlet, Pressure outlet, Wall and Symmetry. Viscous model was defined as Spalart-Allmaras for the fluid flow, solver as Fluent 5/6 and mesh type as QUAD [14]. Inlet pressure of 0.3 MPa (3 Bar) and inlet temperature values of 300K were given as input. The iteration values were set was about 1000 initially and iterated until the solution converges [15]. Then results were plotted for pressure. Courant number controls the time step used by Fluent during inner iterations performed during each time step. Sl No Nozzle Parameters Values 1 Inlet diameter mm 2 Outlet diameter 16.0 mm 3 Distance between inlet and outlet mm 4 Inlet pressure 0.3 MPa 5 Gauge pressure 0.1 MPa 6 Exit velocity/mach 1Mach 7 Initial inlet gas temperature 300K Table 1: C-nozzle dimensions and process parameters Table 2 shows boundary conditions applied for C- nozzle for carrying out CFD trials Figures 3 and 4 shows C - nozzle without and with presence of co-axially fitted MDT where model and mesh were generated using Gambit software of Fluent. MDT boundary was considered as a wall. For plotting Mach number/pressure, an area at nozzle exit was considered with height more than 2 times exit diameter of nozzle (50 and length was taken as 300mm. Hence a chamber like design was considered with PRESSURE-OUTLET boundary condition as ambient pressure (applied atmospheric pressure of 0.1MPa). This was to adopt similar domain condition as that of wind tunnel experiments [16]. A C- nozzle without any parallel portion is termed as nozzle-a and convergent nozzles with 2mm and 6mm parallel portion attached at its end (duct without change in area) are termed as nozzle-b, nozzle-c respectively. These nozzles used for carrying out the CFD trails are shown in Fig. 3 and Fig 4. Fig 3: C- nozzle (protrusion length is 0 with mesh and applied boundary conditions Fig. 2: C- nozzle dimensions with MDT (with 2 MM protrusion length) Sl No Boundary Conditions Values 1 applied at inlet PRESSUE_INLET 2 applied at outlet PRESSURE_OUTLET 3 applied at axis SYMMETRY 4 WALL 5 applied at nozzle wall applied for MDT WALL 6 MDT Dimensions OD = 8 mm ID = 6 mm t=1 mm 7 Effective length of MDT (15+2) 17 mm 8 Atomizing gas used Nitrogen 9 applied to liquid metal Velocity-Inlet 10 Courant number 0.1 CFL Table: 2 s applied for C-nozzle Fig 4: C-nozzle of protrusion length 2mm (with mesh) III. TEST CASES CONSIDERED FOR PRESENT ANALYSIS Different cases considered for conducting experiments on C- nozzle to measure optimum pressure required for gas atomization process as discussed below: A. Case-1 (Figure: 5) A Type nozzle: Protrusion length of 0 mm. Inlet pressure applied is 0.3 MPa (0.3 Inlet gas temperature is 375K (pre-heated to avoid freezing of gas and melt) Figure 5 shows pressure distribution plot for C-Nozzle for an inlet pressure of 0.3 MPa. In this case, a pressure of 0.15 MPa was obtained at nozzle exit which was greater than atmospheric pressure. This pressure does not cause flow reversal at the nozzle exit. This is the favorable pressure for gas atomization process. When protrusion length of MDT is 2 MM and if aspiration pressure may be optimum, which helps in melt All rights reserved by 363

4 H. Case-8 1) C - type nozzle: Protrusion length is 6 mm. 2) Inlet pressure applied is 0.7 MPa (7 Fig 10: C-nozzle with protrusion length of 6 mm (nozzle with mesh) Figures 11, 12 and 13 shows that when protrusion length increases from 2mm to 6mm, aspiration pressure also increases and this pressure (0.18 MPa [1.8 bar] more than atmospheric pressure) may not be favorable for gas atomization process. F. Case-6 1) C Type nozzle: Protrusion length of 6 mm 2) Inlet pressure applied is 0.3 MPa (3 Here the nozzle exit pressure was found to be around 0.18 MPa (1.80. This nozzle exit pressure is more for gas atomization When protrusion length increases from 2mm to 6mm, aspiration pressure also increases and this pressure may not favorable for gas atomization process. Fig 12: Pressure plot when Pi=7 bar (Protrusion length is 6 Here the nozzle exit pressure was found to be around 0.28 MPa (2.80. This nozzle exit pressure is more for gas atomization Protrusion Nozzle Inlet Nozzle Exit Nozzle Length Pressure Pressure Type ( (MPa) (MPa) C C C Table 4: Protrusion length v/s Nozzle exit pressure (PL = 6 As shown in figure 13, (both experimentation and numerical), as atomization pressure increases, aspiration pressure also increases [1]. Fig 11: Pressure plot when Pi=3 bar (protrusion length is 6 G. Case-7 1) C Type nozzle: Protrusion length is 6 mm. 2) Inlet pressure applied is 0.5 MPa (5 Here the nozzle exit pressure was found to be around 0.22 MPa (2.20. This nozzle exit pressure is more for gas atomization Fig 11: Pressure plot when Pi=5 bar (protrusion length is 6 Fig 13: Aspiration pressure v/s Atomization process Both modeling and experimental results also show that as applied gas pressure increases, aspiration pressure also increases. Cui et al. (2003) have carried out pressure measurements for the gas jet exiting at an angle of 15 from the vertical axis, which is close to the set-up used in the present investigation. They also observed that aspiration pressure decreases with increase in protrusion length from 0 to 6mm, and aspiration pressure increased with increase in atomization pressure from 5 bar to 7 bar [1,11]. It is also observed that, with increase in applied gas pressure, magnitudes of minimum and maximum pressure change but their locations do not change. The effect of protrusion length can be deduced by comparing the pressure profiles at a fixed applied gas pressure. It can be seen that by increasing the protrusion length from 0mm to 2mm the stagnation point shifts to a shorter distance and stagnation pressure increases for all the applied gas pressures. However, the location of minimum pressure does not change with protrusion length; it remains between 2mm and 3mm for All rights reserved by 365

International Journal of Current Engineering and Technology E-ISSN 2277 4106, P-ISSN 2347 5161 2016 INPRESSCO, All Rights Reserved Available at http://inpressco.com/category/ijcet Research Article Analysis

International Conference on Manufacturing Science and Engineering (ICMSE 2015) Optimization of Hydraulic Retarder Based on CFD Technology Li Hao 1, a *, Ren Xiaohui 1,b 1 College of Vehicle and Energy,

STUDY OF NOZZLE INJECTOR PERFORMANCE USING CFD Vimal Kumar Pathak 1 and Sumit Gupta 2 1,2 Department of Mechanical Engineering, MNIT, Jaipur ABSTRACT The aim of this paper is to study the performance of

Proceedings of the th IASME/WSEAS International Conference on FLUID MECHANICS and AERODYNAMICS Drag Characteristics of a Pickup Truck according to the Geometry JONGSOO HA, SHIGERU OBAYASHI, and YASUAKI

PIV ON THE FLOW IN A CATALYTIC CONVERTER APPLICATION NOTE PIV-016 The study and optimization of the flow of exhaust through a catalytic converter is an area of research due to its potential in increasing

Ventilation 1 EFFECTS OF LOCAL AND GENERAL EXHAUST VENTILATION ON CONTROL OF CONTAMINANTS A. Kelsey, R. Batt Health and Safety Laboratory, Buxton, UK British Crown copyright (1) Abstract Many industrial

1 In this lecture... Nozzle: Fixed and variable geometry nozzles Functions of nozzles Thrust vector control Thrust reversal Noise control 2 Exhaust nozzles Nozzles form the exhaust system of gas turbine

Send Orders for Reprints to reprints@benthamscience.ae The Open Mechanical Engineering Journal, 2014, 8, 587-593 587 Open Access Analysis of Flow Field for Automotive Exhaust System Based on Computational

International Journal of Scientific and Research Publications, Volume 4, Issue 4, April 2014 1 Numerical Investigation of Convective Heat Transfer and Pressure Loss in a Round tube Fitted with Circular-Ring

INNOVATION AND DEVELOPMENT OF A HIGH PRESSURE WATER NOZZLE DISCHARGED WITH CURTAIN SPRAY FOR OIL LEAKAGE IN OFFSHORE MUHAMMAD NADZIR BIN NORDIN Report submitted in partial fulfillment of the requirements

icbst 2014 International Conference on Business, Science and Technology which will be held at Hatyai, Thailand on the 25th and 26th of April 2014. AENSI Journals Australian Journal of Basic and Applied